Ok, got you. So at least two real locations where you'd need recruitment: primary/secondary schools and medical establishments.
Tough if you don't have any connection or IRB approvals through any of these places in particular. I'd think it would be easiest to work your way down from the top through a district school administration and a hospital research office. Again, tough if you're not a member of either of these places. I will be curious to see if you get any other useful feedback (this forum, unfortunately, is not particularly engaged). I really do think that the best way to do this without any sort of available monetary incentive is direct communication with administrators who can be convinced that your work is relevant and worthwhile to pass on down their bulk e-mail lists.
My previous participant recruitment was generally through paid studies so unfortunately I have limited knowledge in such a thing. Hope you get the data you need.